It is well known that paperboard used for milk and juice containers can be economically coated with heat and pressure sensitive thermoplastic substances. Such substances must be inert to the substances to be packaged, strong and durable, inexpensive, and easy to apply in sheet form onto the paperboard. One example of a suitable thermoplastic substance, useful for packaging dairy products, is polyethylene.
The paperboard stock for forming the containers is initially supplied in the form of rolls. As the stock is produced it is coated on both sides with layers of polyethylene of predetermined thicknesses. Blanks are then cut from the thus treated paperboard roll, and scored so as to be adaptable to being folded into a tubular shape with readily foldable and sealable leak-proof top and bottom closures. Generally, it has been desirable for the finished bottom end closure to contain at least three plies of stock at each bottom corner area, with a minimal length of raw edge exposed to the interior of the container and, hence, to the contents thereof.
A very satisfactory and widely used container and infolded bottom closure is that shown and described in Egleston et al. U.S. Pat. No. 3,120,335.
In view of the fact that a considerable volume of thermoplastic coated paperboard is used for the packaging of milk and juices on today's market throughout the world, it is desirable to save as much paperboard as possible while maintaining the current high standards for efficiently manufacturing a high quality, leak-proof, sanitary container.